How to make beer foam
I would animate a simple UVWarp with a texture with transparency.

I would model the foam as a single object, not detailed at all. Look for a texture with transparent parts, apply it to the foam object. Apply a UVWarp modifier to the object (this modifier moves the texture), and animate the modifier using an armature and two bones. 

The texture should have a big transparent part, so when it is animated it looks like if its going down from nothing. Pretty sure it could do the trick for a couple of seconds.